Researchers from Rice University and Baylor College of Medicine (BCM) have broken one of the major roadblocks on the path to growing transplantable tissue in the lab: they have found a way to grow the blood vessels and capillaries needed to keep tissues alive. The new research is available online and in the January 2011 issue of the journal Acta Biomaterialia, and was supported by the National Science Foundation and the NIH.
“The inability to grow blood-vessel networks—or vasculature—in lab-grown tissues is the leading problem in regenerative medicine today,” said lead co-author Dr. Jennifer West of Rice University. As its base material, a research team chose polyethylene glycol (PEG), a nontoxic plastic that is widely used in medical devices and food. Building on 10 years of research in Dr. West’s lab, the scientists modified the PEG to mimic the body’s extracellular matrix—the network of proteins and polysaccharides that make up a substantial portion of most tissues. They combined the modified PEG with 2 kinds of cells—both of which are needed for blood-vessel formation. Using light that locks the PEG polymer strands into a solid gel, they created soft hydrogels that contained living cells and growth factors. After that, they filmed the hydrogels for 72 hours. By tagging each type of cell with a different colored fluorescent marker, the team was able to watch as the cells gradually formed capillaries throughout the soft, plastic gel. To test these new vascular networks, the team implanted the hydrogels into the corneas of mice, where no natural vasculature exists. After injecting a dye into the mice’s bloodstream, the researchers confirmed normal blood flow in the newly grown capillaries. Another key advance involved the creation of a new technique called “2-photon lithography,” an ultrasensitive way of using light to create intricate 3-dimensional patterns within the soft PEG hydrogels. West said the patterning technique allows the engineers to exert a fine level of control over where cells move and grow. In follow-up experiments, also in collaboration with the Dickinson lab at BCM, Dr. West and her team plan to use the technique to grow blood vessels in predetermined patterns.
(Source: Rice University, January 12, 2011)